This invention relates to the transfer of impressions from one surface to another and more particularly to the transfer of pressure applied impressions by the use of coatings.
Coatings for the transfer of impressions are typically formed from waxes or wax-like materials, to which a colorant or blend of colorants has been added. Other materials are added when special properties are desired. The ensuing mixture is then generally applied to a substrate such as paper either in molten form or in solution with one or more organic solvents. In the case of a paper substrate the resulting product is commonly known as carbon or transfer paper. The product is also known as "one-time" carbon paper when it is intended for a single use.
The usual manufacturing procedure for transfer coatings and their products is relatively slow and cumbersome. Their ingredients are costly and in short supply. In addition special equipment is required when the coatings are applied in molten and organic solvent form. Moreover, the coatings formed on product substrates tend to be relaatively thick. By comparison with the results from using thinner or harder coatings, the transfer images from relatively thick coatings typically have reduced definition, particularly when used to form a large number of copies.
Attempts have been made to avoid the objections of organic solvent coatings by using aqueous or water soluble coating formulations. One such example is set forth in U.S. Pat. No. 2,931,752. However, the coatings produced in accordance with that patent continue to employ costly raw materials which are now in short supply and have reduced image definition by comparison with standard coatings of comparable thickness.
Aqueous coatings have also been used in the production of donorreceptor copy papers to provide what is commonly known as "mated" systems. One example is U.S. Pat. No. 3,635,747. Not only are there the disadvantages and waste of the mated system, the transfer images again, tend to have reduced definition.
Similarly in Swiss Pat. No. 465,386 and German Pat. No. 1 421 444 the use of aqueous coatings is accompanied by production and technical disadvantages as well as a failure to obtain the desired image definition.
Accordingly it is an object of the invention to expedite the manufacture of transfer coatings and their products. A related object is to expedite the production of coatings for transfer media such as carbon papers.
A further object of the invention is to increase the flexibility with which transfer coatings and their products can be manufactured. A related object is to permit the manufacture of transfer media such as carbon papers directly in conjunction with the operation of a paper making machine, or as an adjunct to the paper making process.
Still another object of the invention is to avoid the equipment complexities of molten and organic solvent coating systems. A related object is to adapt aqueous coating equipment to the manufacture of transfer media while improving the quality and image definition achievable with the resulting product.
A still further object of the invention is to reduce the overall cost of the raw materials employed in the production of coatings for transfer media. A related object is to reduce the extent of the conventional materials employed in transfer coatings, without impairing image definition.
Yet another object of the invention is to achieve a comparatively low cost aqueous coating system which provides improved image definition.